Photo Credit: Jason Weingardt

West Kaua’i

Today: Breezy. Mostly cloudy with isolated showers. Highs around 82 near the shore to around 68 above 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 68 near the shore to around 59 above 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy with scattered showers. Highs around 82 near the shore to around 69 above 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Kaua’i

Today: Breezy. Mostly cloudy with numerous showers. Highs 76 to 82. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with numerous showers. Lows around 68. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Wednesday: Breezy. Mostly cloudy with numerous showers. Highs 76 to 82. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Breezy. Occasional showers. Highs 68 to 75 in the valleys to around 60 above 4000 feet. East winds 10 to 25 mph. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers. Lows 61 to 66 in the valleys to around 56 above 4000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain near 100 percent.

Wednesday: Breezy. Occasional showers. Highs 68 to 75 in the valleys to around 60 above 4000 feet. East winds 10 to 25 mph. Chance of rain near 100 percent.

North Kaua’i

Today: Breezy. Mostly cloudy with occasional showers. Highs 70 to 82. East winds 10 to 20 mph. Chance of rain 90 percent.

Tonight: Breezy. Cloudy with occasional showers. Lows 61 to 70. East winds 10 to 20 mph. Chance of rain 90 percent.

Wednesday: Breezy. Occasional showers. Highs 70 to 82. East winds 10 to 20 mph. Chance of rain near 100 percent.

East Kaua’i

Today: Breezy. Occasional showers. Highs 67 to 79. Northeast winds 10 to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers. Lows 61 to 72. Northeast winds 10 to 20 mph. Chance of rain near 100 percent.

Wednesday: Occasional showers. Highs 67 to 79. Northeast winds 10 to 15 mph. Chance of rain near 100 percent.

Detailed Forecast

Synopsis

A couple of high pressure areas passing far north of the islands will maintain locally windy trades through about Thursday. Moisture riding in on the trades, combined with a trough aloft to the northwest of the islands, will keep skies cloudy and the trades rather wet through the next few days. Most showers will focus windward and mauka, but many leeward areas will have a shower from time to time as well. Drier and more settled weather, with increasing sunshine is expected to arrive for the holiday weekend as high pressure aloft builds over the main Hawaiian Islands.

Discussion

Bands of low level moisture (1.2 to 1.35 inches on CIMSS MIMIC- TPW imagery) caught up in the trades are continuing to bring plenty of showers to the islands very early this morning, with the more persistent showers continuing to focus on Kauai, Oahu, and Molokai. Instability from relatively steep low-level lapse rates continues to be a factor in enhancing shower activity, although the 12z Lihue sounding showed a little less boundary layer instability. Trades continue to be locally windy, with Lihue reporting sustained 24 kt at 12z. The trades are being driven by a 1027 mb high about 800 mi NNW of Kauai. The subtropical jet is carrying considerable high cloudiness eastward across the islands from a TUTT out near the date line, and these have been very slowly increasing and thickening with time.
The next few days look to continue this spell of relatively cool, cloudy, and at times showery pre-Christmas weather in Hawaii. The surface high will push very slowly E and strengthen a couple of mb through Wed, keeping trades locally windy. Haven't had any new NASA SPoRT 89 GHz microwave imagery overnight, which helps reveal the locations of upstream showery cloud bands through the increasing high cloud deck. Yesterday's visible and 89 GHz satellite imagery showed a band headed our way a few hundred miles to the NW, and the various high resolution and global models suggest this next loosely-organized batch should get to the islands about Wed. Although guidance shows low-level lapse rates becoming more shallow and stable as it arrives, increasing moisture aloft should instead help enhance the showers as they come into the islands. Any limited breaks of sunshine Tue should give way to mainly overcast skies as high clouds overtop of the showers thickens up.
After Wed, a new, stronger high moving E from the west Pacific will merge with the first high, and pass about 1100 mi N of Honolulu on Thu. The TUTT to the W will weaken and push E toward the islands during the latter half of the week. Low level moisture should decrease some on Wed into Thu, but models suggest there might be a weaker band of showers coming through about Fri (mainly near Maui and the Big Island), but some showers expected between the bands. Any details on timing, intensity, or location of shower bands gets more fuzzy as you go farther out in time, but the general idea is that the trades will continue to be rather wet through about Thu night or perhaps into Fri.
Heading into the holiday weekend and toward Christmas Day, the trough aloft pushes past the islands, allowing increasingly strong ridging aloft to take over. This should bring the wet trade wind pattern to a rather abrupt end, and the layered high and mid level clouds should finally diminish leading to some very pleasant weather with lots of sunshine for most areas. Starting about Friday, the trades will very gradually diminish day-by-day as a subtropical ridge develops N of the islands in the wake of the 2nd surface high, reaching gentle to locally breezy levels by Christmas.

Aviation

Locally windy continue to bring showers across the western end of the state this morning. While windward areas have been the primary focus, showers are still spilling over to some leeward locations. AIRMET Sierra is in effect for tempo mountain obscuration for north through east sections of Kauai, Oahu, Molokai and Maui through this morning, and may be needed through the period for some locations if showers persist.
Trade winds are still on track to strengthen slightly today and remain elevated through mid week. This will result in some moderate low-level turbulence over and downstream of the island terrain for the next couple of days. AIRMET Tango is now in effect for leeward areas of all islands. In addition, a jet streak aloft is bringing areas of moderate turbulence over the islands. AIRMET Tango remains in effect for tempo moderate turbulence between FL240 and FL350. These conditions may persist as the tail end of the jet streak lingers over the islands today into Wednesday.
Furthermore, a layer of deep moisture riding in on the jet streak over the islands is producing some light precipitation at higher levels in the atmosphere, which could lead to light icing on aircraft flying through the layer from about 14000 ft to 23000 ft.

Marine

Surface high pressure centered approximately 700 nautical miles north-northwest of Kauai is pressing down a tight enough pressure gradient across the islands to maintain generally water-wide fresh to locally strong trade winds. The morning ASCAT pass verified these magnitudes and, when combined with elevated seas created by Monday morning's large northeast swell passage, an all water Small Craft Advisory (SCA) is still warranted. A slowly declining northeast swell with incoming northwest swell under fresh trades has the SCA in effect through Wednesday afternoon. Trades should remain at least high-end moderate to locally strong within various channels and bays through Thursday before dropping to more moderate to fresh speeds Friday as a result of the high drifting further eastward.
Monday's large northeast swell reached its peak about 24 hours ago and has been on a steady slow decline. The swell still remains elevated enough today, at around 8 feet in the medium period spectral bands, to warrant a east-facing shore High Surf Advisory (HSA) in effect through the afternoon. North-facing shores will receive a small, medium period northwest swell through the day that will hold well below advisory level surf through Thursday afternoon. A larger northwest swell is scheduled to arrive late Thursday that will likely lift north surf up to HSA levels as it peaks out early Friday. Periods of very small, long to medium period south to southwest swell will keep south-facing shore surf from going completely flat this week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Olomana, Kauai East, Koolau Windward, Molokai Windward, Molokai Southeast, Windward Haleakala, Kipahulu, Big Island East, Big Island North.
Small Craft Advisory until 6 PM HST Wednesday for all Hawaiian waters,

Data Courtesy of NOAA.gov